When a low-resolution image is to be displayed on a high-resolution display device, the low-resolution image (original image) is subjected to a scaling-up process, and the image having subjected to the scaling-up process is displayed on the high-resolution display device, enabling the low-resolution image (original image) to be displayed as a high-quality image. When a scaled-up image (an image having subjected to a scaling-up process) is to be subjected to a process for improving image quality, information about how much magnification has been used is necessary, and accuracy in estimation of this information affects the image quality.
Typically, when an image having SD (Standard Definition) quality is scaled up to an image (video) having HD (High Definition) quality in a display device such as a television set, the factor of scaling-up (hereinafter referred to as a “scaling-up factor”) in the scaling-up process may be easily grasped because the resolution of the original image before the scaling-up process is already known.
However, for example, when a video or the like which has been scaled up by a broadcasting station is received, the number of pixels of the received image (video) is equal to the number of pixels for an HD image (HD video). Therefore, the magnification for the image (video) before a scaling-up process is not typically known. Therefore, in this case, it is necessary to estimate the scaling-up factor.
In a method of related art in which a scaling-up factor is estimated, an image signal is directly subjected to frequency analysis (for example, a Fourier transform), whereby high-frequency components included in the image signal are detected, and an approximate scaling-up factor is estimated on the basis of the amount of the detected high-frequency components.
For example, a technique disclosed in PTL 1 (Japanese Unexamined Patent Application Publication No. 2000-305555) enables the number of horizontal pixels of a video (image) to be estimated by using a horizontal synchronization signal and a vertical synchronization signal as key information. Therefore, the technique enables a scaling-up factor to be estimated.